This invention relates to flowmeters, and more particularly to a turbine flowmeter having considerable versatility without any electromagnetic rotor drag or stalling tendencies.
In the past the pick-up of a turbine flowmeter has been constructed of an inductive winding about an axis of symmetry and about a permanent magnet core. The prior art flowmeter is then provided with a non-magnetic conduit or cylindrical tube through which the fluid flows. The pick-up is fixed to the tube with the pick-up axis normal to the tube axis. An inclined plural blade rotor is then mounted inside the tube at a position along the length thereof where the pick-up is located. Each rotor blade is made of a ferromagnetic material and thus induces a voltage pulse in the winding as each blade passes the winding. Sometimes the blades are permanently magnetized in addition to or in lieu of the core magnetization. In any case, the number of pulses so generated is then approximately proportional to the total volume flow through the tube. Uses for this type of instrument as meters and otherwise are set forth in U.S. Pat. Nos. 3,756,079 and 3,842,655. By this reference hereto, the entire contents of said U.S. Pat. Nos. 3,756,079 and 3,842,655 are incorporated herein as though fully set forth hereat.
Notwithstanding the utility of conventional turbine flowmeters, they have several very serious disadvantages. In the first place, the magnetization of the core or blades causes an error producing drag on the rotor because of the magnetic force of attraction between the ferromagnetic rotor blades and the ferromagnetic core especially at low flow rates. Moreover, at certain low flow rates, the rotor actually stalls and completely fails to generate any pulses because of the said magnetic force of attraction. In other words, the meter completely fails to operate.
Still another very serious disadvantage of conventional turbine flowmeters is that the rotor blades thereof must always be made of a ferromagnetic material which may be incompatible with the fluid, the flow of which is to be metered. The rotor blades may thus, for example, be corroded or eaten away entirely.